IEC 62368-1: Ask the Engineers, Question-and-Answer Page

General

Does UL Standards and Engagement plan to publish a UL 62368-3 Standard based on IEC 62368-3:2017?

For those unaware, the first edition of IEC 62368-3 was published in 2017, and has the title, Audio/video, information and communication technology equipment - Part 3: Safety aspects for DC power transfer through communication cables and ports. It addresses two key topics. 

Clause 5 covers power transfer using ES1 and ES2 voltages. USB and PoE are examples of the technologies covered.

Clause 6 covers power transfer using RFT, or Remote (Power) Feeding Telecommunications circuits. Clause 6 essentially covers the same circuits / technologies as originally covered in the legacy standard, IEC 60950-21, Remote Power Feeding.

For more background on IEC 62368-3, please review UL Solutions IEC 62368-3 Backgrounder.

When the CAN US Technical Harmonization Committee (THC) reviewed both IEC 62368-1:2018 and IEC 62368-3:2017 for potential adoption in Canada and the U.S., a decision was made to develop and propose a CAN US version of the IEC 62368-1:2018 standard, which subsequently was published on December 13, 2019 as CSA UL 62368-1:2019 (Ed. 3). However, during this review the THC also made a decision not to pursue a CAN US version of IEC 62368-3.

The decision not to pursue a CAN US version of IEC 62368-3 was made because the THC believed IEC 62368-3 requires some refinement before it would be an appropriate standard for adoption as a mandatory bi-national standard for Canada and the U.S. This refinement was thought needed both for its Clause 5 and its Clause 6. Therefore, rather than adopt IEC 62368-3, the THC proposed, and eventually got accepted the following National Difference in Clause 1 of CSA UL 62368-1, Ed. 3.

“1DV.2.3 Additional requirements for equipment with DC power transfer through communication cables and ports are given in IEC 62368-3. IEC 62368-3 clause 5 for DC power transfer at ES1 or ES2 voltage levels is considered informative. IEC 62368-3 clause 6 for remote power feeding telecommunication (RFT) circuits is considered normative (see ITU K.50). Alternatively, equipment with RFT circuits are given in either UL 2391 or CSA UL 60950-21. RFT-C circuits are not permitted unless the RFT-C circuit complies with RFT-V limits (<= 200V per conductor to earth).”

Therefore, in Canada and the U.S., USB, PoE and similar circuits will not be required to be investigated to Clause 5 (in addition to 62368-1). However, RFT circuits will continue to need additional evaluation beyond 62368-1 per the options allowed for in the National Difference 1DV.2.3.

Note, within IEC TC108 there are two projects open to replace IEC 62368-3 Clause 5 with a new IEC 63315 and Clause 6 with a new IEC 63316, both of which will be Group safety publications.

General

I am interested in joining IEC TC108 and assisting with the development of IEC 62368-1 - how can I do this?

Experts / Manufacturers generally do not join the IEC Technical Committees independently.  Typically, a Manufacturer should first join their National Committee (NC) for IEC and begin getting involved participating in their National Committee.  National Committee members receive IEC TC108 documents, can propose comments/revisions (if the NC supports them), and can participate in their National Committee voting. Please note, most National Committees will have an associated monetary fee to participate.

Subsequently, as an NC member, if the NC Member is interested, the Member can request to join as an Expert the IEC TC maintenance teams, new work project teams, etc., including the Hazard Based Standard Development Team, which does the primary work maintaining IEC 62368-1, producing documents for NC review and voting. All formal approval of documents is via National Committee voting.

Therefore, we recommend that you contact the National Committee that represents your country if your country participates on IEC TC108 - https://www.iec.ch/dyn/www/f?p=103:29:717472019271837::::FSP_ORG_ID,FSP_LANG_ID:1311,25.

 In the US, the associated TC108 committee is the ANSI US NC / Technical Advisory Group (TAG) for IEC TC108 - https://www.ansi.org/usnc-iec/usnc-overview. As UL Standard and Engagement is the Secretary of the US TAG TC108, you can contact ULSE for additional information on joining the US TAG TC108 - https://62368-ul-solutions.com/contact-ul.html.

Clause 0 Principles of this product safety standard

Why is HBSE (Hazard-Based Safety Engineering) called the future of product safety?

Hazard-based safety engineering (HBSE) offers a new perspective on product safety. HBSE principles permeate the new IEC 62368-1 safety standard, and are primarily performance-based, rather than prescriptive. Fewer prescriptive requirements means you don’t need to wait so often for standards to catch up with innovation. A hazard-based standard devoid of prescriptive construction requirements and containing only performance-oriented requirements to determine the effectiveness of required safeguards means that a higher level of flexibility now exists for product designers as product technologies and constructions continue to evolve.

Clause 1 Scope

Can UL 62368-1 be used to certify/list Modular Data Centers (MDCs) in the United States?

The short answer is, no.

In the U.S., modular data centers, or MDCs, are installed in accordance with NFPA 70, the National Electrical Code (NEC).

In fact, in the 2014 NEC, a new Article 646, Modular Data Centers, was added specifically to cover MDCs. So, any jurisdiction (state or otherwise) in the U.S. that has adopted the 2014 NEC (or later) will require the MDC to be installed per NEC Article 646.

A MDC is defined in the NEC as a Prefabricated unit, rated 1000 volts or less, consisting of an outer enclosure housing multiple racks or cabinets of information technology equipment (ITE) (e.g., servers) and various support equipment, such as electrical service and distribution equipment, HVAC systems, and the like.

Thus, Article 646 covers, or points to requirements for electrical supply and distribution, HVAC, lighting / emergency lighting, IT/ITC equipment, and other aspects.

While via an Informational Note in the Article it acknowledges UL 62368-1 as the appropriate standard for certification of the actual IT/ICT equipment installed in a MDC, UL 62368-1 does not cover MDCs under its scope, nor does it address the key support equipment mentioned above also found in a typical MDC.

What Article 646 does acknowledge (in 646.4) is that MDCs that are listed and labeled in compliance with UL Subject 2755, Outline of Investigation for Modular Data Centers, only require specific, limited areas of Article 646 to be applied to them in addition. This is because UL Subject 2755 is aligned with the requirements in Article 646 and covers many of the MDC construction elements not found in UL 62368-1, including requirements for the support equipment.

UL Solutions offers listing and labeling to UL Subject 2755 under our PQVA equipment category.

Clause 1 Scope

Is outdoor AV/ICT equipment covered by (UL EN) IEC 62368-1?

In IEC 62368-1:2014, the scope (Cl 1) referenced IEC 60950-22 for AV/ICT equipment that may be installed outdoors.

However, as of Edition 3 (IEC 62368-1:2018), the requirements for outdoor AV/ICT equipment are incorporated into the Part 1 Standard, and there will not be a separate Part 2 standard like there was for IEC 60950.

Annex Y (Construction requirements for outdoor enclosures) contains most of the requirements found previously in IEC 60950-22, but other clauses also incorporate some requirements, such as Clause 5 and voltage limit considerations for accessible contact of potentially wet parts.

The current editions of EN IEC 62368-1 and CSA UL 62368-1 are structured similarly.

Clause 1 Scope

Does the IEC 62368-1 standard cover lead-acid batteries?

In response, since there are no product details provided with your question, including what type of lead-acid batteries (e.g., VRLA, flooded, etc.) are used and what type of AV/ICT equipment will the batteries be installed within, the response to your inquiry will rely mainly on quoting the requirements in IEC 62368-1:2018 that address AV/ICT equipment with lead-acid batteries.

However, first, the simple answer to your question is, yes, IEC 62368-1:2018 (and IEC 62368-1:2023) covers AV/ICT equipment containing lead-acid batteries.

On the component level, lead-acid batteries used in AV/ICT equipment should comply with the applicable component standards noted in Annex M.2, such as IEC 60896-11 (Stationary Lead Acid Batteries – Part 11 – Vented type); IEC 60896-21 (Stationary Lead Acid Batteries – Part 21 – Valve regulated type – method of test); IEC 61056-1(General purpose lead-acid batteries (valve-regulated types) – Part 1: General requirements, functional characteristics – Methods of test); and IEC 61056-2 (General purpose lead-acid batteries (valve-regulated types) – Part 2: Dimensions, terminals and marking).

Table 17, Safety of batteries and their cells - requirements (expanded information on documents and scope), of IEC TR 62368-2, Audio/video, information and communication technology equipment – Part 2: Explanatory information related to IEC 62368-1:2018, provides a good overview of the standards in Annex M.2 that cover lead-acid batteries.

On the equipment level, the requirements for equipment with lead-acid batteries are included in the following Annex M sub-clauses: (a) Annex M.3 - protection circuits for batteries provided within the equipment; (b) Annex M.5 – risk of burn due to short-circuit during carrying; (c) Annex M.6 – safeguard against short-circuits; (d) Annex M.7 – risk of explosion from lead acid and NiCd batteries; (e) Annex M.8 – protection against internal ignition from external spark sources of rechargeable batteries with aqueous electrolyte; (f) Annex M.9 – preventing electrolyte spillage; and (g) Annex M.10 – instructions to prevent reasonably foreseeable misuse.

Due to the limited information in your question, only a general response has been able to be provided to your inquiry. However, we encourage you to contact UL Solutions for an in-depth consultation related to specific applications that involve use of lead-acid batteries in AV/ICT equipment.

Clause 4 General requirements

Are all power supplies rated 60 VDC or less required to comply with IEC 62368-1 when used in AV/ICT equipment?

More specifically, you asked (edited for clarity): Do all power supplies regardless of isolation level or output voltage require compliance to IEC 62368-1 when used in an information technology or AI processor module board? For example, do all the following power supplies require compliance to IEC 62368-1: an intermediate stage power supply with rated input 40-60V DC and with output 5-7.5 Vdc, 1kW; followed by a second stage(s) operating from 5 to 7.5V on the input and producing 1V, 900A on the output (or multiple supplies in parallel adding to 900A)?

In response to the question, we refer to the Standard IEC 62368-1:2023.

There are a variety of drivers for certification (compliance) to IEC 62368-1, which are separate from the decisions made on application of the standard itself. For a manufacturer of a power supply, including a multi-stage power supply as described, the drivers to consider for certification (compliance), even if not clearly regulation driven, may be a customer requirement, competitive marketing advantage, supply chain simplification, or similar. Feel free to reach out to UL Solutions to discuss this aspect in more detail.

Related to application of IEC 62368-1 and whether parts of the Standard apply to the different components of the overall power supply system described in the question, the fact that the power supply is rated maximum 60V DC does not limit application of the Standard. The following considerations illustrate this.

From an electric shock perspective (Clause 5), the fact that the power supply input and output are classified ES1 (60 V DC or less) does not mean there are no requirements in Clause 5 with respect to electric shock. It is noted that DC/DC converters may generate internal voltages above 60 V DC that may be classified ES2, or even ES3, which require safeguarding. Therefore, there may be requirements in Clause 5 applicable to DC/DC converters as described, including the need for classification and, when applicable, appropriate safeguards. While some constructions may require performance and/or construction compliance, others may be deemed to require no safeguards as described in clause 5, for example when a review concludes that all circuits are ES1.

From a fire hazard perspective (Clause 6), classification of circuits also is required regardless of low voltages, and the fact the DC/DC converter has an output rated 900A assures there will be PS2 and PS3 circuits involved. Such DC/DC converters, including its components and materials, will require a Basic Safeguard, per sub-clause 6.3, as a minimum (min. flammability ratings, restricted temperatures during normal and abnormal operating conditions), and may require Supplementary Safeguards when PS2 or PS3 circuits are involved, including the option for a fire enclosure (per 6.4.5 and 6.4.6) when using Control of Fire Spread method. The example construction, with a 900A output, thus PS3 class, would require all associated components and materials to be evaluated per the requirements in sub-clause 6.4.6. Additional component requirements also may apply to, for example (but not exclusively), printed circuit boards (national difference for USA/Canada), wiring flammability ratings, transformer per sub-clause G.5.3, including overload.

Touch temperatures (Clause 9) during normal, abnormal and single fault conditions also may be evaluated when a part of DC/DC converter is determined accessible, for example, a heatsink or a partial enclosure that is intended to serve as end-product enclosure.

As this forum is not intended to analyze and provide guidance on specific designs, we recommend that you contact UL Solutions and request an in-depth consultation if you have a specific design or construction that you would like to discuss.

Clause 4 General Requirements

What temperature limit and other safeguard criteria should be used for the enclosure of a class III product?

More specifically, you asked (edited for clarity): What should be used as the temp limit for the plastic enclosure of an ES1 product during the temperature measurement test? Sub-clause 6.3.1 indicates max component temps should be 90% of the spontaneous ignition temp, or 300C, while IEC TR 62368-2 (in 6.3) explains that RTI (Relative Thermal Index) is not considered appropriate. Other safeguard properties are ensured by safeguard robustness tests. Our interpretation is that plastic enclosure temps would be limited by touch temp, ignition temp, and passing of the T.8 Stress Relief.

In response to the question, we refer to the Standard IEC 62368-1:2023.

It is noted that temperature measurements typically are conducted for the purpose of determining compliance with the following sub-clauses:

-5.4.1.4: Maximum operating temperatures for materials, components and systems, but which usually are not considered applicable for class III products.

-6.3: Safeguards against fire under normal operating conditions and abnormal operating conditions, for which 90% of the spontaneous ignition temperature, or 300 C is used. RTIs are not considered appropriate for the purpose of sub-clause 6.3 as explained in IEC TR 62368-2.

-9.3: Touch temperature limits, for which limits of Table 38 are used based on type of accessible surface material and expected time of contact (and regardless of RTI of the surface material).

Additionally, an enclosure made of rigid thermoplastic material and used as safeguard may be subjected to the following sub-clauses, as applicable:

- 4.4.3: Safeguard robustness, including Stress Relief Test per sub-clause T.8;

- Y.6: Mechanical strength of enclosures (outdoor equipment).

In addition to above, when plastic materials are used for compliance via preselection (e.g., UL Recognized Component Plastic), the RTI associated with a covered rating (e.g., flammability) typically will be a consideration.

Alternatively, the flammability test methods in Annex S of IEC 62368-1 may be used.

As this forum is not intended to analyze and provide guidance on specific designs, we recommend that you contact UL Solutions and request an in-depth consultation if you have a specific design or construction that you would like to discuss.

Clause 4 General requirements

Do Suppliers of components (actives and passives) to power supply manufacturers and equipment manufacturers need to certify to 62368-1 and what are those tests required?

Your question seems to be related to general component requirements and supply chain transition plans to IEC 62368-1, which would be challenging to fully answer / explain in this sort of Q&A forum. 

However, the component requirements in IEC 62368-1 usually are specified in Annex G, Components, although there are a few special components that have their own Annex, like Annex J, for multi-layer insulated winding wire.

Components in 62368-1 generally are considered several different ways. They need to either:

• comply with a specified IEC component standard (e.g., X/Y capacitors, fuses, varistor, switches, etc.), which generally need certification to the IEC component standard; or
• comply with the IEC 62368-1 requirements (e.g., motors, IC Current Limiters, etc.), usually included as a performance test program in Annex G; or
• comply with either a specified IEC component standard specified in Annex G or a test program in Annex G (e.g., transformers, opto-coupler, etc.).

If a component is listed in Annex G, generally it is preferable that the component manufacturer achieve component certification to allow for pre-selection by the end product manufacturer.  The component certification is either by certification to the IEC component standard, if a standard other than IEC 62368-1 is specified (e.g., X or Y capacitor), or by certification to IEC 62368-1 (e.g., IC Current Limiter).

If IEC 62368-1 does not specifically reference an IEC component program or an Annex G performance program, then the component generally can be investigated as part of the equipment without any special investigation (i.e., does not require individual certification) – this applies to most passives, including resistors, electrolytic and film capacitors (non- X & Y), inductors, transistors, etc. not used as a safeguard.

In the U.S. and Canada there are specific component requirements for some components, which are contained in Annexes DVE, DVF & DVG. For example, printed circuit boards associated with ES 2/ 3 and PS 2/ 3 circuits need to comply with UL 796.

For detailed requirements for components, please review Annexes G, DVE, DVF & DVG, and we encouraged you to contact UL Solutions for an in-depth consultation via https://www.ul.com/services/iec-62368-1-testing-certification.

Clause 4 General requirements

What are the requirements for internal and external wiring according to IEC 62368-1, Ed. 3, and UL 62368-1, Ed. 3?

More specifically, you asked: I am seeking product certification to IEC 62368 and have come up against the wire flammability issue. I note the existing answer regarding equivalence with VW-1, but what about superior standards such as CL2? Is there a means by which CL2 being superior — i.e., the NEC® allows substitution — to VW-1 allows me to demonstrate compliance with UL 62368, the Standard for Audio/Video, Information and Communication Technology Equipment?

In response, as you inferred, the note under Subclause 6.5, “Internal and external wiring” in IEC 62368-1, Ed. 3, as well as UL 62368-1 accepts VW-1 wires rated to UL 2556, the Standard for Wire and Cable Test Methods, to demonstrate compliance with 6.5.1 as an alternative method.

In addition, for external wiring, according to the U.S./CAN deviations under 4.1.17DV.1, “External interconnecting cable and wiring,” such wiring is to be investigated to the requirements of 6.5 and either 4.1.17DV.1.2 or 4.1.17DV.1.3, depending on the cable length.

External interconnecting cable and wiring 3.05 m or less may be investigated as part of the equipment (system) to the requirements of this standard, depending on the PS circuits involved:

• External interconnecting cable and wiring connected to PS2 or PS3 circuits — the flammability requirement of 6.5 applies.
• There are no flammability requirements for external interconnecting cable and wiring in PS1 circuits.

Other external interconnecting cables and wiring exceeding 3.05 m in length are required to comply with 4.1.17DV.1.3, including the references to the Canadian Electrical Code, Part I, CSA C22.1; and the National Electrical Code® (NEC®), NFPA 70®, under Annex DVA (Annex Q), where CL2 Listed cables are allowed to be used in Class 2 and LPS circuits.

Such CL2 cables are UL Listed as Power Limited Circuit Cable (QPTZ), information for which can be found in UL Product iQ®.

Please note: CL2 cables are subjected to a vertical-tray flame test in UL 1685, the Standard for Vertical-Tray Fire-Propagation and Smoke-Release Test for Electrical and Optical-Fiber Cables, which is a more onerous test than VW-1. Therefore, if a manufacturer wanted to also substitute Listed CL2 cables for internal wiring or external cabling not exceeding 3.05m in length, that would be considered acceptable, too, as long as the circuit was Class 2 or LPS. However, most manufacturers choose not to do so due to cost considerations.

The complete answer to this topic is complex, and there appears to be a specific, detailed construction that needs review/analysis. Therefore, we encourage you to contact UL Solutions for an in-depth consultation.

Clause 5  Electrically-caused injury

How are the spacings determined on inner surfaces of a PCB (classified as Material Group I), and what tests are applicable to this insulation?

More specifically you asked (edited for clarity): If the CTI of the PCB is >=600 (i.e., Material Group I), would the Creepage distance requirement on the inner surfaces of a PCB be taken from the column for pollution degree 2 and material group 1 of Table 17? If so, can I assume that as per 5.4.4.5 a), no other tests are required to be done on the PCB assembly to determine compliance if the specified clearances are provided?

In response, sub-clause G.13 of IEC 62368-1 covers printed boards, commonly also referred to outside IEC standards as printed circuit boards (PCB). Its G.13.4, Insulation between conductors on the same inner surface, states, “On an inner surface of a multi-layer printed board (see Figure O.14), the path between any two conductors shall comply with the requirements for a cemented joint in 5.4.4.5.”

Sub-clause 5.4.4.5, Insulating compound forming cemented joints, essentially provides three options for considering such cemented joints, either (a) provide Clearances and Creepage distances for Pollution Degree 2, (b) provide Clearances and Creepage distances for Pollution Degree 1, or (c) apply Distance through insulation requirements.

Related to 5.4.4.5 a), which covers the Pollution Degree 2 situation asked in your question, for a PCB with a CTI of 600 or greater, the Creepage distances would be determined by utilizing the column for Material Group I and Pollution Degree 2 in Table 17. No other tests are required to be determine compliance, if the required minimum Clearances and Creepage distances are provided, although the insulation between the different inner layers of the PCB also must comply with an electric strength test per 5.4.9.

Though the question specifically asked about Pollution Degree 2, sub-clause 5.4.4.5 b) is another option where spacings no less than required for Pollution Degree 1 need to be met. The Creepage Distance can be determined by utilizing the column for Pollution Degree 1 in Table 17. However, one sample also is required to pass the test of 5.4.1.5.2, Test for pollution degree 1 environment and for an insulating compound, unless the printed board is made of pre-preg and the temperatures on the board measured during the heating test of 5.4.1.4 do not exceed 90°C. Also, again, the insulation between the different inner layers of the PCB also must comply with an electric strength test per 5.4.9.

For both 5.4.4.5 a) and b), please also consider, since a required Creepage distance cannot be less than a required Clearance (as covered in 5.4.3.1), if the value for Creepage distance obtained from Table 17 is less than the required Clearance, the required Creepage distance is to be equal to the required Clearance.

The final option, sub-clause 5.4.4.5 c), allows for smaller spacings (i.e., 0.4mm) as noted in 5.4.4.2, Minimum distance through insulation, if three samples pass the test of 5.4.7, Tests for semiconductor components and for cemented joints. However, again, if the PCB is made using pre-preg and the temperatures measured during the heating test of 5.4.1.1 do not exceed 90°C, the test of 5.4.7 would not be required.

As this forum is not intended to analyze and provide guidance on specific designs, we recommend that you contact UL Solutions and request an in-depth consultation if you have a specific design or construction that you would like to discuss.

Clause 5 Electrically-caused injury

Why do the IEC 62368-1 Table 17 Creepage Distance working voltages start at 10V RMS for Basic Insulation when 10V is ES1 and does not require a Creepage Distance?

The spacings tables in clause 5.4 provide clearance and creepage distance values for the specified voltages regardless of ES energy classification. These values are based on the IEC 60664 series insulation coordination standards. The need to apply minimum clearance and creepage distances within ES1 circuits depends on the specific requirement being applied. For example, clause B.4.4, Functional Insulation, is an example of when such spacings would be considered within ES1 circuits as one option.

As this forum is not intended to analyze and provide guidance on specific designs, we recommend that you contact UL Solutions and request an in-depth consultation if you have a specific design or construction that you would like to discuss.

Clause 5 Electrically-caused injury

For a DC power supply of 48V input, is it necessary to list X capacitors connected across the input in the critical component list (CCL) - if yes then what is the safety aspect of listing them?

In response, since 48Vdc is classified as ES1 when any related tolerances of the supply circuit are less than 60Vdc, the criteria in Table 4 for ES1 would be met. In such a case no further safeguard would be required for such X capacitors, and 5.5.2.1 and G.11 would not apply. Therefore, such X capacitors should not need to be listed in the CCL in most cases.

As there appears to be a specific, detailed construction that needs review / analysis that may not be obvious from the details in the question (e.g., if specified tolerances were greater than 60Vdc, and therefore the requirements and limits in clause 5.5.2.2, Safeguards against capacitor discharge after disconnection of a connector, also may need to be considered), you are encouraged to contact UL Solutions for an in-depth consultation via https://www.ul.com/services/iec-62368-1-testing-certification.

Clause 5 Electrically-caused injury

How is ES class evaluated for a DC to DC switching power supply? Can a measured voltage determine ES class when DC is supplied?

More specifically you asked (edited for clarity): How to evaluate ES class associated with a DC to DC switching power supply? It seems not suitable to test its touch current because, according to 5.7.2, it is based on IEC 60990, which mainly covers AC distributed power. if DC supplied, do we only measure voltage to determine ES class?

In response, electrical energy source (ES) classifications are determined by voltage or current according to sub-clause 5.2. Table 4 defines the ES limits for steady state voltage and current. It’s applied for both AC and DC. Also, footnote “c” states, “For sinusoidal waveforms and DC, the current may be measured using a 2 000 Ω resistor.”

If DC output voltage exceeds ES1 limit (60V), then current should be measured using a 2 k Ω resistor, but compliance with both voltage limits and current limits is not required. Note also that ES1 is defined when the measured value does not exceed ES1 limits under normal, abnormal operating and single fault conditions (or when not exceeding ES2 limits under single fault conditions of a Basic or Supplementary Safeguard).

Related to applicability of IEC 60990 to DC, although most of the example supply circuits in IEC 60990 are AC, the Scope (1) of IEC 60990 covers, “…measurement methods for - d.c. or a.c. current of sinusoidal or non-sinusoidal waveform, which could flow through the human body…,” and “…is applicable to all classes of EQUIPMENT, according to IEC 61140.” IEC 61140 covers both AC and DC systems. However, as stated above, IEC 62368-1, Table 4, footnote “c” allows use of a 2 000 Ω resistor rather than an IEC 60990 network for DC and sinusoidal AC. For simplicity, a 2 000 Ω resistor typically is used for DC touch current measurements.

When DC-DC converters are involved, the evaluation and classification is not limited to the voltage levels of the circuit supplying the converter - the working voltages and frequency generated within the converter also need to be considered. For example, when accessible circuits are required to be ES1 due to some accessibility requirements in the final application, the entire system and its circuits must be analyzed by construction review and, when required, by measurement and tests, such as Working Voltage Measurement and Single Fault Condition (SFC), to demonstrate that the ES1 circuits are not compromised by higher ES2 or ES3 voltages generated within the converter. Investigation and test may show that additional Safeguards are required.

With reference to sub-clauses 4.2.3 and 4.2.4, it also is important to note that the standard allows manufacturers to declare higher class than there is in the product. (For example, if an energy source class 3 is declared by the manufacturer, there is no need to conduct any ES1 or ES2 measurements, assuming ES1 is not required because of accessibility.)

Also, specifically related to switch-mode power supplies, as an ES classification is based on working voltage and/or touch current, it is worth noting that voltages (due to switch-mode conversion) may be generated that exceed the ES1 limit even if the input to the supply is ES1. Therefore, detailed evaluation and tests typically are needed for such switch-mode conversion circuits, even for DC-DC converters. However, for most converters, such as 5V input to 3.3V or 1 Vdc output, typical switching voltages are not expected to exceed ES1 limits under normal, anormal or single fault conditions.

Clause 5 Electrically-caused injury

How is a Clearance determined when the working frequency is above 30 kHz for a switch mode power supply according to IEC 62368-1:2018?

More specifically you asked (Edited): In Edition 3, for determining a clearance, Table 10 should be used for the switching frequencies not exceeding 30 kHz and Table 11 for those exceeding 30 kHz. Since most power supplies would generate switching frequencies greater than 30 kHz, Table 11 is necessary to follow. For an overvoltage category II, PD 2, Material Group III, this value jumps from 1.27 mm in Table 10 and to 13.2 mm in Table 11 for > 30kHz. Please let me know if my understanding is correct. Also please confirm, whether these "switching frequencies" are of the "mains voltage" or of the "working voltage" of the power supply? Primary? Secondary?

In response, for determining Clearances per 5.4.2, the highest value of two procedures is used. Your question is specifically related to Procedure 1, determining Clearances according to 5.4.2.2, which considers the highest voltage of either the Working Voltage (across the Clearance), Recurring Peak Voltages, and the Temporary Overvoltage.

More specifically, the highest voltage is used to determine the Clearance, using Table 10 for circuits with fundamental frequencies up to 30 kHz, Table 11 for circuits with fundamental frequencies higher than 30 kHz, and both Tables 10 and 11 for circuits where both frequencies lower and higher than 30 kHz are present.

When Table 10 applies, the temporary overvoltage 2000V should be considered, and for the conditions you stipulated, we confirm a 1.27 mm Clearance would be the resulting minimum Clerance for basic or supplementary insulation.

When Table 11 applies, which is only applicable for those voltages with working frequencies higher than 30 kHz, the voltage associated with the switching frequency generated from pulse-width modulation (PWM) in the primary circuit of the power supply should be applied rather than a temporary overvoltage, which does not have a frequency higher than 30 kHz.

Therefore, the clearance result you indicated of 13.2 mm (based on a temporary overvoltage value of 2000V used in Table 11) would be incorrect. Generally, most applications of switch mode power supplies would result in a peak working voltage in the primary circuit not exceeding 1000 V, resulting in a Clearance from Table 11 of 0.6 mm for basic or supplementary insulation.

However, the highest clearance values of Table 10 and Table 11 should be chosen for circuits where both frequencies lower than 30 kHz and higher than 30 kHz are present in Procedure 1. Therefore, the result from Table 10, 1.27 mm Clearance would be the highest for the Procedure 1. However, values per Procedure 2 also need to be considered as part of the final determination.

We expect you would find very helpful subclause 5.4.2 of IEC TR 62368-2:2019, which is the Technical Report (TR) containing explanatory information on IEC 62368-1 and is often known as the ‘Rationale Document.’ This sub-clause 5.4.2 contains a very good flowchart / worked example on the application of the Clearance requirements.

Clause 5 Electrically-caused injury

I calculated the clearances according to 5.4.2.1 and got the highest value according to Procedure 1. Now I want to find the test voltage from Table 16. Can I use 5.4.2.3.2.5 for decreasing the required withstand voltage to get lower test voltage?

All references are to the published IEC 62368-1: 2014, unless otherwise indicated.

You indicated that you calculated the clearances according to 5.4.2.1 and got the highest value according to Procedure 1. Then you indicate you want to find the test voltage from Table 16.

Please note, per 5.4.2.1, to determine the Clearance, the highest value of the two procedures is used, Procedures 1 and 2.

Table 16 is associated with 5.4.2.4 Determining the adequacy of a clearance using an electric strength test. Sub-clause 5.4.2.4 is part of Procedure 2 (the alternative approach if Procedure 2 is larger than Procedure 1).

However, since you indicated you already got the highest value according to Procedure 1, there is no need to use Procedure 2 and 5.4.2.4 (Clearance per Procedure 1 + ES). You can use Procedure 1 without Electric Strength.

Please look at the flowchart in 5.4.2 of IEC TR 62368-2, Explanatory information related to IEC 62368-1. It illustrates nicely the relationship between Procedures 1 & 2.

Note, you also reference 5.4.2.3.2.5, Determining transient voltage levels by measurement,  but this sub-clause only is used if you do not want to use the assumed transient voltages per Table 13. It is not used for withstand voltage.

Clause 5 Electrically-caused injury

Why did UL 62368 not use UL 101 method ("e" is always open) to measure touch current? What's the background?

UL 62368-1 is harmonized with IEC 62368-1.  As an electronic standard it utilizes the leading information on assessment of electric shock.  As part of this it follows the testing protocol of IEC 60990, Methods of measurement of touch current and protective conductor current.

62368-1 also considers risk to a person under normal, abnormal and single fault conditions.  This is a basic principle within the Standard.  In line with this philosophy, IEC 60990 considers the various faults possible based on power distribution system (single phase, 3 phase Delta, etc.) and power systems, e.g., TN, TT, etc.

An aid is available to all users of IEC 62368-1, it is the technical report IEC TR 62368-2, Explanatory information related to IEC 62368-1:2018.  Within this document it explains how hazard-based engineering was followed and  resulted in the development of the requirements.  The document can be purchased through your regular standard acquisition channels.

In addition to the rationale document, there are a number of technical papers available on the development of IEC 60990 and its principles.

Clause 5 Electrically-caused injury

Must external protective earthing conductors be provided with Class I permanently connected equipment powered by DC mains, or may on-site installation of such PE conductors be required by user documentation?

More specifically you asked: For permanently connected equipment powered by DC mains, using an external protective earthing conductor: Is the manufacturer expected to provide this protective earthing conductor as part of the equipment or can the specifications and/or use of such a conductor be stated in the user documentation?

There is a variety of equipment types powered by DC mains, so we cannot answer your question in great specificity in this public Q&A platform. Therefore, you are encouraged to contact UL Solutions for an in-depth consultation via https://www.ul.com/services/iec-62368-1-testing-certification.

However, in general, yes, permanently connected equipment may have a protective earthing conductor that is installed in the field by skilled persons (electricians).

Such field wiring can consist of both line conductors and PE conductor(s). Electricians who install the equipment will provide suitable wiring materials necessary for the supply and PE connections in accordance with the installation instructions associated with the equipment (and in accordance with national/local electrical codes). However, proper interface with the electrical system (mains) is required as part of the equipment, which includes not only instructions, but also proper terminal sizes, etc.

In IEC 62368-1:2018, appropriate requirements primarily are in sub-clause 5.6, Protective Conductor. Equipment can either be shipped with the appropriate PE conductor(s) complying with the relevant requirements in sub-clause 5.6, or be provided with installation instructions so that the installers can select proper wiring material for the field installation.

In CSA UL 62368-1, appropriate National Differences that reflect the US and Canadian electrical codes are in Regulatory Annex DVA, 5.6, including the provision that “Equipment intended to be connected to a nominal 48 V d.c. (or higher) power supply source, or systems rated less than 48 V d.c. that have one point directly earthed (grounded), shall have provision for the earthing (grounding) of all exposed dead metal parts that might become energized from the power supply source or from circuits involving a risk of electric shock.” Additional National Differences are in Annex DVH, Requirements for permanent connection, and associated Marking and Instruction requirements are in Annex DVK.

Clause 5 Electrically-caused injury

Does pluggable type B equipment with an Ethernet port need to be provided with a permanently connected protective earthing conductor to comply with the requirements in Sub-clause 5.6.7?

More specifically you asked (edited for clarity): In sub-clause 5.6.7, whether pluggable equipment type B is considered to have reliable earthing seems to depend on if it connects to external circuits ID 1 to 5. Would pluggable type B equipment with an Ethernet port need to have provision for a permanently connected protective earthing conductor to comply? Is it of any significance if, (1) the Ethernet connector shield is or is not connected to earth in the equipment?; (2) the equipment does or does not have varistors connected directly between mains and earth?; (3) the Ethernet, or other external circuits ID 1 to 5, do or don't extend outside the building?

In response, the intention of sub-clause 5.6.7 is that it only is to be considered when other sub-clauses in IEC 62368-1:2018 require reliable earthing and reference 5.6.7 for requirements. Sub-clause 5.6.7 does not establish when reliable earthing is required since that determination is made by other sub-clauses which reference 5.6.7. Therefore, whether AV/ICT with an Ethernet port requires reliable earthing is not based on sub-clause 5.6.7, but by other sub-clauses.

If another sub-clause requires reliable earthing and references 5.6.7, and the subject equipment is Pluggable Type B (or even Pluggable A) with circuits considered Table 13, ID numbers 1, 2, 3, 4 or 5, then 5.6.7 requires a permanently connected Protective Earthing Conductor (separate from the earthing associated with the plug), with instructions for the installation of that separate conductor to the building earth by a Skilled Person. However, please also note that most Ethernet ports with paired conductor cabling are not considered IDs 1 or 2 (per Table 13) subjected to transients if the cable is not intended (by installation instructions or similar) to be routed outside the building. (See first condition of Table 13.) 

We note that these requirements have been updated in IEC 62368-1:2023.

The complete answer to this topic is complex, and there appears to be a specific, detailed construction that needs review/analysis. Therefore, you are encouraged to contact UL Solutions for an in-depth consultation via https://www.ul.com/services/iec-62368-1-testing-certification.

Clause 5 Electrically-caused injury

Does UL 62368-1 allow use of a green colour insulation for a protective bonding conductor?

More specifically you asked: In sub-clause 5.6.2.2 (Colour of insulation), can protective bonding conductors be insulated with a green colour (not green-and-yellow) except for the two cases in this sub-clause? I know that protective earthing conductor could be insulated with a green colour according to the National Difference in UL 62368-1 in G.7. How about protective bonding conductor?

In response, sub-clause 5.6.2.2 requires green-and-yellow for the insulation of both protective earthing conductor(s) and protective bonding conductor(s). The green (only) colour of insulation only is permitted in the protective earthing conductor of power cord sets in North America. As you stated, this requirement is in Annex DVE (G.7) of UL 62368-1.

Since a protective bonding conductor is defined per 3.3.11.9 in UL 62368-1:2019 (3.3.11.8 in UL 62368-1:2014) as being located in an equipment, it is not a part of the power supply cord. Thus, the insulation of the protective bonding conductor is not covered by Annex DVE (G.7) and is required to be green-and-yellow, except for the two cases indicated in sub-clause 5.6.2.2 accordingly.

Clause 5 Electrically-caused injury

For determining Clearances, is it allowed to reduce mains transients by using either external or internal surge protection devices?

More specifically you asked (edited for clarity): I have a question concerning clearance requirement in sub-clause 5.4.2.3.2.2, Determining AC mains transient voltages: “In general, clearances in equipment intended to be connected to the AC mains, shall be designed for Overvoltage Category II. Equipment that is likely, when installed, to be subjected to transient voltages that exceed those for its design overvoltage category requires additional transient voltage protection to be provided external to the equipment.” Question: Whether the phrasing “shall be designed for Overvoltage Category II” is always required despite the fact that the sentence begins with the words in general? Is it allowed to use lower mains transient value to reduce the clearance by using external surge protection module in mains supply side? How about internal surge protection?

In response, although it is unclear from your question whether the equipment subjected to the enquiry is equipment installed indoors or outdoors, it is noted that requirements in IEC 62368-1:2018 now consider both indoor and outdoor applications, whereas in IEC 62368-1:2014 it only covered indoor applications (with outdoor applications covered by IEC 60950-22).The outdoor locations requirements from IEC 60950-22 have been incorporated into IEC 62368-1:2018, including those that impact requirements for surge protection devices and consideration of transient voltages.

Sub-clause 5.4.2.3.2.2 in IEC 62368-1:2018 currently is clear that installed equipment likely to be subjected to transient voltages that exceed those for its design overvoltage category (e.g., OV Cat II) requires additional transient voltage protection to be provided “external” to the equipment, in which case, the installation instructions shall state the need for such external protection. Currently, in 5.4.2.3.2.2 of IEC 62368-1:2018 it does not mention use of such protection inside the equipment.

However, also keep in mind, subclause 5.4.2.3.2.1 states, transient voltages can be determined based on their origin, or can be measured in accordance with 5.4.2.3.2.5. If additional surge suppression to address reduced overvoltage category was provided inside the equipment, it is likely that measurement of actual transient voltages per 5.4.2.3.2.5 would be expected / required since the type of surge suppression installed externally typically is different than those installed internally. However, 5.4.2.3.2.5 also requires that surge suppressors internal to the equipment in circuits connected to the mains to be disconnected, which likely would invalidate the advantages of placing surge suppression inside the equipment for most applications.

The complete answer to this topic is complex, and there appears to be a specific, detailed construction that needs review/analysis. Therefore, you are encouraged to contact UL Solutions for an in-depth consultation via https://www.ul.com/services/iec-62368-1-testing-certification.

Clause 5 Electrically-caused injury

For two varistors connected between both sides of Mains (L & N) and Protective Earthing (PE) through the same GDT, is it acceptable that each varistor withstands a voltage based on half of equipment input voltage rating?

More specifically you asked: For a product with input voltage 100-240 Vac submitted for UL CSA IEC 62368-1 evaluation, does Annex G.8.1 allow using two MOVs between L and N with a midpoint connection to PE through a GDT, if each varistor’s Maximum Continuous Voltage (MCOV) rating (e.g., 215 Vac) passes 1.25 times the half of rated voltage ( 240 / 2 * 1.25 = 150 Vac) of equipment, so therefore the sum of the two varistors (e.g., 215 Vac + 215 Vac = 430 Vac) in series has a total MCOV of greater than the minimum required voltage (240 Vac * 1.25 = 300 Vac) per the upper voltage of the Rated Voltage Range of the equipment?

(L-PE is MOVA+GDT; N-PE is MOVB+GDT; and L-N is MOVA+MOVB)

The construction under discussion consists of two varistors connected between Line and Neutral with a GDT connected midpoint between the two varistors and Protective Earthing. When the GDT is activated, this results in a varistor and GDT in series between L and PE (MOVA+GDT) and a varistor and a GDT in series between N and PE (MOVB+GDT), and, when the GDT is not activated, two varistors in series between L and N (MOVA+MOVB).

In response, per sub-clause 5.5.7, where an SPD is used between the Mains and Protective Earthing, it shall consist of a varistor and a GDT connected in series and the varistor shall comply with Clause G.8 in Annex G.  Per G.8.1, the MCOV of a varistor shall be at least 1.25 times the Rated Voltage (or the upper voltage of the Rated Voltage Range) of the equipment.

With above scenario, the MCOV rating of each varistor of the two is required to be at least 1.25 times the upper voltage of the Rated Voltage Range of the equipment. For the example given, the MCOV rating of each varistor should be at least 300 Vac (i.e., calculated by 240 Vac * 1.25). Therefore, a varistor rated 215 Vac (i.e., less than 300 Vac) is deemed not sufficient per the presently published requirements in Annex G.8.1.

(Note, the currently published requirements are based primarily on consideration of the overvoltage implications of the L or N to PE effects and not the L to N effects. Any proposal (with technical rationale) to adjust this would need to be subjected to the IEC committee expert review process and should be proposed to IEC TC108.)

The complete answer to this topic is complex, and there appears to be a specific, detailed construction that needs review/analysis. Therefore, you are encouraged to contact UL Solutions for an in-depth consultation via https://www.ul.com/services/iec-62368-1-testing-certification.

Clause 5 Electrically-caused injury

Does sub-clause 5.4.5 of UL IEC 62368-1 (Ed. 3) apply to both a device connected to an outdoor antenna and an indoor device with a small integral antenna, like a wireless router? Why does a test voltage of 10kV apply?

More specifically you asked (edited for clarity): For the purposes of testing insulation, sub-clause 5.4.5 in Ed. 3 states that the insulation between mains and antenna terminals, and mains and external circuits providing non-mains supply to equipment having antenna terminals, shall withstand electrostatic discharges at the antenna terminals. Is this requirement applicable to any type of antenna? I do not understand why the accessible terminal is tested 50 times at 10kV while the accessible conductor on a USB or ethernet port or similar component is tested against a different voltage. Is clause 5.4.5 only meant for outdoor antenna or would the tiny antenna on an indoor wireless router also need to be tested if it is supplied by a mains power module? And if so, what are the dangers addressed in the case of small indoor devices with tiny antennas such that regular insulation tests are inadequate to deal with it?

In response, sub-clause 5.4.5 of IEC 62368-1:2018 (Ed. 3) does not apply to equipment connected to every type of antenna. The requirement does not apply to indoor devices with an indoor antenna (e.g., on the wireless router). The test voltage applies between mains and any terminals directly or indirectly connected to an outdoor antenna only. For equipment connected to an outdoor antenna, the specified insulation is required to withstand electrostatic discharges because a high voltage (up to 10kV) caused by electrostatic charge may accumulate over time on the outdoor antenna due to environmental effects, like dust blowing against the outdoor antenna. For a more detailed background of this requirement, please consult sub-clause 5.4.5 in the “Rationale document”, IEC TR 62368-2:2019.

Clause 6 Electrically-caused fire

Does a DC bus bar that can carry 48 V, 6000 A (ES1, PS3) need a fire enclosure?

More specifically, you asked (edited for clarity): If a device has DC bus bars that can carry 48 V and 6000 A (ES1, PS3) and the bus bars (multiple, stacked together) are separated by an insulator having a flammability rating of V-0 at the thickness used, would the bus bars need to be encased in a fire enclosure per IEC 62368-1? The standard doesn't necessarily delve into busbars.

In response, although the bus bars are operating at 48 VDC and are not a risk of electric shock (ES1), they are carrying greater than 100 VA, so they are a risk of fire (PS3) per Clause 6, Electrically-caused fire.

Furthermore, since the available power of the circuit exceeds 4000 W, per sub-clause 6.4.1 the reduce the likelihood of ignition option for safeguarding against fire under single fault conditions is not permitted. Therefore, per sub-clause 6.4.1 the control fire spread option needs to be applied for such safeguarding against fire under single fault conditions, which per sub-clause 6.4.6 requires a fire enclosure to be provided in accordance with sub-clause 6.4.8 (among other considerations specified in the sub-clause). So, for the described construction, yes, a fire enclosure is required per IEC 62368-1 Clause 6.

Additionally, sub-clause 4.9, Likelihood of fire or shock due to entry of conductive objects, has additional consideration for PS3 circuits, including reference to Annex P, Safeguards against conductive objects.

Also noteworthy in the context of bus bars, IEC 62368-1 does not have requirements for safeguarding from a 240 VA energy hazard that was previously located in sub-clause 2.1.1.5 of IEC 60950-1. Please refer to IEC TR 62368-2, Explanatory information related to IEC 62368-1, under Clause 5 for a complete explanation why.

As this forum is not intended to analyze and provide guidance on specific designs, we recommend that you contact UL Solutions and request an in-depth consultation if you have a specific design or construction that you would like to discuss.

Clause 6 Electrically-caused fire

What are the requirements for fire enclosure openings when a product can be positioned in multiple orientations?

More specifically, you asked (edited for clarity): We would like to ask about the requirements for ventilation openings for the heat transfer and protection against the fire risk. If we want to design our product to be in both vertical and horizontal orientations, what requirements should we follow?

In response, the UL 62368-1, Edition 3 requirements for fire enclosure openings are specified in sub-clause 6.4.8.3 and equipment orientation is specified in sub-clauses 4.1.4 and 4.1.6.

Fire enclosure opening requirements are dependent upon their proximity to a Potential Ignition Source (PIS). Per sub-clauses 4.1.4 and 4.1.6, where it is clear that the orientation of use of equipment is likely to have a significant effect of the application of the requirements, all orientations of use specified in the installation or user instructions are required to be taken into account. However, if the equipment has means for fixing in place by an Ordinary Person, such as screw holes for direct attachment to a mounting surface through the use of mounting brackets, either provided with or readily available on the market, all likely positions of orientation are to be taken into account, including mounting to a non-vertical surface regardless of the installation instructions provided by the manufacturer. These orientations would need to be taken into account when determining whether an enclosure opening is considered a top, bottom or side opening with regards to their proximity to a PIS.

Top opening requirements are specified in sub-clause 6.4.8.3.3, bottom opening requirements are specified in sub-clause 6.4.8.3.4, and side opening requirements are specified in sub-clause 6.4.8.3.6. Please note that side openings also may be considered bottom openings if they are within a 5 degree downward projection from the PIS as noted in Figure 44.

Also, in the latest edition, IEC 62368-1:2023, there has been some refinement of the construction requirements for fire enclosure and fire barrier openings throughout sub-clause 6.4.8.3, so it is recommended that you review the latest changes. Please refer to the UL Solutions’ Certification Impact Analysis: IEC 62368-1:2023 (Edition 4) for additional insight.

As this forum is not intended to analyze and provide guidance on specific designs, we recommend that you contact UL Solutions and request an in-depth consultation if you have a specific design or construction that you would like to discuss.